This invention relates to a facsimile apparatus capable of subjecting facsimile communication information to cryptographic processing.
Conventional facsimile communication is carried out by a transmission control procedure in accordance with CCITT advisory T.30, and a major characteristic thereof is that a facsimile apparatus is capable of communicating with an unspecified large number of other facsimile apparatus via a public telephone transmission network.
For specific users, such as governmental offices and banks, it is required that the contents of facsimile communications be kept confidential because of the nature of the work carried out.
In order to maintain the confidentiality of a communication, the conventional practice for such users is to connect an encrypting device to the facsimile apparatus. Such a device encrypts the contents of a communication before transmission in order to prevent the leakage of information if the apparatus is inadvertently connected to a facsimile apparatus other than that intended, as by dialing in the wrong number, or if the telephone line of the apparatus is wire-tapped.
A facsimile apparatus capable of such encrypted communication according to the prior art will now be described with reference to FIG. 5.
The facsimile apparatus having the construction shown in FIG. 5 will be described taking as an example a case where the apparatus sends image information to another facsimile apparatus 60 via a transmission line 51, a public telephone transmission network 50 and a transmission line 52 in accordance with an input from a control panel 14.
A conventional facsimile apparatus of this type transmits all communication information following encryption.
In operation, an encrypted control signal, which has been transmitted at a transmission rate of, say, 300 bps from the other facsimile apparatus 60, which is the facsimile apparatus on the receiving side, via the transmission line 52, public telephone transmission network 50 and transmission line 51, is sent to a demodulating circuit 8 from an NCU 6. The control signal demodulated by the demodulating circuit 8 enters a decoder 17-b, where the encrypted data is restored to the original data that is then transmitted to a received-data control circuit 9. The control signal that has been restored to the original data is deframed by the received-data control circuit 9, after which the resulting data is analyzed by a control-signal analyzer 10. The output of the analyzer 10 is sent to a flow controller 11, which administers overall control of the facsimile apparatus in accordance with a control procedure stored in a ROM 12.
In accordance with the control signal analyzed by the control-signal analyzer 10, the flow controller 11 causes a control-signal generator 2 to generate a corresponding control signal to be sent to the receiving side. The control signal generated by the control-signal generator 2 is directed through a changeover circuit 3 and sent to a transmission-data control circuit 4, where the control signal is subjected to framing processing. Thereafter, the output of the control circuit 4 is sent to a coder 17-a, where prescribed encryption processing is executed. The encrypted information is modulated by a modulating circuit 5 and is then transmitted to the other facsimile apparatus 60 on the receiving side via the NCU 6.
When such pre-processing has thus been executed prior to transmission of an image signal, the image signal, which is read by a reader 1 (or an image signal that has already been stored in a RAM 13), is obtained from the changeover circuit 3 and is then encrypted by the coder 17-a and transmitted to the other facsimile apparatus 60 in accordance with a route similar to that of the control signal described above.
On the receiving side, the received image signal is sent from the NCU 6 to the demodulating circuit 8. After the received image signal is demodulated by the demodulating circuit 8, the encrypted data are restored to the original data by the decoder 17-b, and these data are sent to the received-data control circuit 9. The received image signal is subsequently sent to the recorder 15, where the signal is printed out on recording paper or the like.
Thus, in the prior art, all of the communication data are encrypted, and facsimile communication is performed solely by the encrypted data.
However, in the example of the prior art described above, the following problems are encountered since the encrypting device which maintains the confidentiality of a communication is permanently connected to the facsimile apparatus:
(1) In a case where a call is established between the facsimile apparatus and one to which an encrypting device is not connected, one of the apparatus is entirely incapable of understanding the contents of a communication, the communication cannot be performed normally and operation ends in an error, regardless of whether the operation is transmission or reception. Moreover, when such a situation arises, the operator cannot tell why the operation ended in an error. PA1 (2) In order to perform communication with a facsimile apparatus to which an encrypting device is not connected, the operator must search for another facsimile apparatus not having an encrypting device connected thereto or must open the cover of the original facsimile apparatus, detach the cable of the encrypting device and connect a bypass cable in its place. This is a very troublesome operation, especially when it must be repeated often. PA1 (3) Since all control signals are also encrypted, encrypting of procedure signals takes extras time, and therefore an exorbitant amount of time is needed to determine whether communication is possible with another party's facsimile apparatus.